Petroleum products have contaminated groundwater with harmful organic compounds, such as benzene, toluene, ethylbenzene, and xylenes (BTEX). Collecting and analyzing polluted groundwater samples is expensive and undertaken infrequently. However, quick remedial action in case of unexpected events requires continuous monitoring. In-situ water quality sensors (pH, EC, DO, ORP) may show correlations with the components of dissolved petroleum hydrocarbon (PHC) such as aromatics and non-volatile mobile fractions. Correlations are prerequisite to ultimately develop real-time prediction models. Since suitable field data sets are limited, we simulated the fate of hydrocarbons in groundwater under various realistic conditions using a reactive transport model as novel approach to explore when, where, and why correlations occur. A stationary oil source zone continuously dissolved at the top of a heterogeneous and shallow sandy aquifer over a two-dimensional cross-section. Our model considered transient conditions (fluctuating water table) and spatially uniform hydrogeochemical composition. We observed a strong correlation between PHCs and water quality sensors (rolling Spearman's correlation > |0.8|) at varying periods. These correlations are strongly affected by the location of observation wells, the aquifer's hydraulic conductivity, and the availability of calcite and oxide minerals, and other electron acceptors. DO and ORP are significant for the early detection of hydrocarbon contamination, whereas pH and EC are important features for the long-term monitoring of hydrocarbons. Our findings lay the foundation for the subsequent development of a data analysis model to detect and estimate in real time PHC levels in groundwater using in-situ water quality sensors.

中文翻译：

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用于探索水质传感器估算地下水碳氢化合物水平潜力的反应输运模型

石油产品含有苯、甲苯、乙苯和二甲苯 (BTEX) 等有害有机化合物，污染了地下水。收集和分析受污染的地下水样本成本高昂且很少进行。然而，在发生意外事件时快速采取补救措施需要持续监控。原位水质传感器（pH、EC、DO、ORP）可能显示与溶解石油烃 (PHC) 成分（例如芳烃和非挥发性流动馏分）的相关性。相关性是最终开发实时预测模型的先决条件。由于合适的现场数据集有限，我们使用反应输运模型作为探索相关性发生时间、地点和原因的新方法，模拟了各种现实条件下地下水中碳氢化合物的命运。固定油源区在二维横截面的非均质浅层砂质含水层顶部连续溶解。我们的模型考虑了瞬态条件（地下水位波动）和空间均匀的水文地球化学成分。我们观察到不同时期 PHC 和水质传感器之间存在很强的相关性（滚动 Spearman 相关性 > |0.8|）。这些相关性受到观测井位置、含水层导水率、方解石和氧化物矿物以及其他电子受体的可用性的强烈影响。 DO 和 ORP 对于碳氢化合物污染的早期检测具有重要意义，而 pH 和 EC 则是碳氢化合物长期监测的重要特征。我们的研究结果为后续开发数据分析模型奠定了基础，该模型可使用原位水质传感器实时检测和估计地下水中的 PHC 水平。